Neutral organic solute effects on the activity of the plasma membrane Ca2+-ATPase
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We have compared effects of dimethylsulfoxide (Me2SO) and two polyols on the Ca2+-ATPase purified from human erythrocytes. As studied under steady-state conditions over a broad solute concentration range and temperature, Me2SO, glycerol, and xylitol do not inhibit the Ca2+-ATPase activity; this is in contrast to numerous other organic solutes that we have investigated. Under specific experimental conditions, Me2SO (but not glycerol) substantially increases Ca2+-ATPase activity, suggesting a possible facilitation of enzyme oligomerization. The activation is more pronounced at low Ca2+ concentrations. In contrast to glycerol, Me2SO shows no protective effect on enzyme structure as assessed by determining residual Ca2+-ATPase activity after exposing the enzyme to thermal denaturation at 45°C. Under these conditions several other organic solutes strongly enhance the denaturating effect of temperature. Because of the temperature dependence of its effect on the Ca2+-ATPase activity we believe that Me2SO activates the Ca2+-ATPase by indirect water-mediated interactions.
Key wordsCa2+-ATPase purified enzyme erythrocyte Ca2+-ATPase activity dimethylsulfoxide
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